Post-fabrication adjustment of optical characteristics of lenses is needed in various ophthalmic lens types. In one case, cataract patients would benefit from post-implant power adjustability of an IOL implant. In another case, posterior chamber phakic IOLs could benefit from post-implant power adjustability since biometry cannot insure proper power selection. Corneal inlays or similar types of lens also would benefit from implantation of thin plano lenses followed by a later expansion of the lens to provide the desired refractive effect. Also, contact lenses would benefit from post-fabrication curvature adjustment to limit the number of lenses that needed to be maintained in inventories.
Cataracts are major cause of blindness in the world and the most prevalent ocular disease. Visual disability from cataracts accounts for more than 8 million physician office visits per year. When the disability from cataracts affects or alters an individual's activities of daily living, surgical lens removal with intraocular lens implantation is the preferred method of treating the functional limitations.
In the United States, about 2.5 million cataract surgical procedures are performed annually, making it the most common surgery for Americans over the age of 65. About 97 percent of cataract surgery patients receive intraocular lens implants, with the annual costs for cataract surgery and associated care in the United States being upwards of $4 billion.
A cataract is any opacity of a patient's lens, whether it is a localized opacity or a diffuse general loss of transparency. To be clinically significant, however, the cataract must cause a significant reduction in visual acuity or a functional impairment. A cataract occurs as a result of aging or secondary to hereditary factors, trauma, inflammation, metabolic or nutritional disorders, or radiation. Age-related cataract conditions are the most common.
In treating a cataract, the surgeon removes material from the lens capsule and replaces it with an intraocular lens (IOL) implant. The typical IOL provides a selected focal length that allows the patient to have fairly good distance vision. Since the lens can no longer accommodate, the patient typically needs prescription eyeglasses for reading.
The surgeon selects the power of the IOL based on analysis of biometry of the patient's eye prior to the surgery. In a significant number or cases, after the patient's eye has healed from the cataract surgery, there is a refractive error was beyond the margin of error in the biometric systems. Thus, there remain intractable problems in calculating the proper power of an IOL for any particular patient. To solve any unpredicted refractive errors following IOL implantation, the ophthalmologist can perform a repeat surgery to replace the IOL—or the patient can live with the refractive error and may require prescription eyeglasses to correct for both near and distant vision.
The correction of ocular wavefront aberration in ophthalmology is a field of increasing interest. Current diagnostic systems based on the Shack-Hartmann (S-H) wavefront sensors can operate in real time, measuring the aberrations about every 40 msec. Besides the diagnostic speed provided, there are other advantages of these new devices in ocular wavefront aberration measurement, such as the use of infrared light, and the fact that the systems use objective methods to simplify the task of the subject.
At present, the only way to correct ocular aberrations beyond second-order is by customized refractive surgery such as in situ keratomileusis (LASIK). However, the corneal ablation approach will suffer from many problems such as the complexity of controlling corneal biomechanics and healing after surgery, and aberrations probably induced by cutting the corneal flap that enables the ablation procedure.
Preliminary research has been done in correcting aberrations with aspheric customized contact lenses. This approach also faces practically insurmountable problems relating to coupling lenses with eye aberrations: (i) lens flexure will be a problem; (ii) tear film effects will introduce spurious aberrations, and (iii) lens rotations and lens translation will limit the performance of the aberration correction.
In studies on large populations, it has been found that for a 5-mm pupil, the contribution to the total root mean square (RMS) wavefront error of the second order is approximately 70% in highly aberrated eyes and 90% in young healthy eyes. If a lens were provided that could correct include third order and spherical aberrations, the percentage of the population that could benefit from wavefront correction would increase to 90% for highly aberrated eyes and to 99% for normal eyes.
Zernike polynomials are a set of functions that are orthogonal over the unit circle. They are useful for describing the shape of an aberrated wavefront in the pupil of an optical system. Several different normalization and numbering schemes for these polynomials are in common use. Fitting a wavefront to Zernike polynomials allows lens designers to analyze the subcomponent aberrations contained in the total wavefront. Some of the lower order aberrations (also defined as Zernike polynomial coefficients having an order (e.g., to first through fifth order aberrations)) in a Zernike series are prism, sphere, astigmatism, coma, and spherical aberration.
A Zernike equation can include as many or few aberrations as required for an application, for example, with more than 63 aberrations beyond sphere. Further explanations of higher order aberration can be found in the following references: Macrae et al., Customized Corneal Ablation-The Quest for SuperVision, Slack Inc., Thorofare, N.J. (2001); Thibos et al., Standards for Reporting the Optical Aberrations of Eyes, Trends in Optics and Photonics Vol. 35, Vision Science and Its Applications, Vasudevan Lakshminarayanan, ed., Optical Society of America, Washington, D.C. (2000), pp. 232-244; Atchison et al., Mathematical Treatment of Ocular Aberrations: a User's Guide, (2000). For the purposes of this disclosure, the adaptive optic corresponding to the invention is designed for the optional correction of higher order aberrations ranging at least above third order aberrations.
In view of the foregoing, what is needed is a lens system that provides means for post-fabrication or post-implant adjustment of optical characteristics and dioptic power. What also is needed is a lens system that can correct higher order aberrations.